This invention relates to telemetry systems and, in particular, to telemetry systems using suppressed ringing telephone connections.
Published European Patent Application No. 0 474 407 A1 discloses an improved telemetry system in which a utility company is able to monitor utility meters at telephone subscriber locations via telephone loop networks serving the subscriber locations. In the '407 application, this is accomplished via a suppressed ringing connection effected through the central office switch serving the subscriber locations.
The system of the '407 application includes a central office service unit which communicates with a utility controller or computer. The central office service unit connects to the trunk unit of the central office switch via utility telemetry trunks which provide a suppressed ringing connection service. As described in the '407 application, the central office service unit and utility telemetry trunks enable a connection to be made through the switch to a desired subscriber location without ringing the telephone at the location.
Once the connection is established, a meter interface unit connected to the loop network can then be alerted by a message transmitted to the unit. The unit can then be instructed by the utility computer to obtain and report data from a utility meter at the subscriber location.
As further described in the '407 application, where the loop network connected to a subscriber location contains certain types of loop carriers, the suppressed ringing connection may require a short burst of signal in order to initiate the loop carrier so that the desired connection can be made. Furthermore, different loop carriers may require different length burst signals. These signals, however, must be kept relatively short so that they terminate before a connection is made so that no or little ringing occurs at the subscriber location.
In the system of the '407 application, a signal code, i.e., a start signal of specific length (e.g., 0, 20 ms, etc.), is included in the signal transmitted to the switch from the central office service unit. This signal code identifies to the switch the signalling mode (i.e., no signal or burst signal of particular extent) required to be used with the loop network through which the suppressed ringing connection is being established. The presence of the signal code thus enables the switch to invoke the appropriate signalling mode to complete the desired connection.
While the '407 application discloses a beneficial suppressed ringing type telemetry system, the disclosed system suffers from certain drawbacks. One drawback is that the system does not provide a mechanism for automatically identifying the signalling mode of the loop network serving a given subscriber location. While a manual process can be used to make this identification and the resultant signal codes for the identified signalling modes stored for use by the system, this is a time consuming and costly process and may result in inaccuracies.
Additionally, in the system of the '407 application, a given signalling mode is established for each subscriber location. However, if the loop network serving a location should be changed, the established signalling mode may no longer be correct. This can result in connections not being made or in ringing at the subscriber location, both of which are undesirable.
Finally, in the system of the '407 application, the utility computer accesses a utility meter interface at a subscriber location by providing a directory number to the central office service unit. This directory number and other telephone system information related to a subscriber location is supplied to the utility by the telephone company. The utility correlates this telephone system information with its own utility customer information so that there is proper correspondence between directory numbers and the utility customers.
However, directory numbers may change as result of disconnects, requests by subscribers or other circumstances. Also, directory numbers for new subscriber locations may not be readily available for transmitting to the utility. As result, a great deal of manual coordination is required between the utility and the telephone company to ensure proper correlation of the directory numbers to the subscriber locations.
It is, therefore, an object of the present invention to provide a telemetry system which does not suffer from the above drawbacks.
It is a further object of the present invention to provide a telemetry system in which the signalling modes for the loop networks serving the subscriber locations can be easily and automatically determined.
It is a further object of the present invention to provide a telemetry system in which the suppressed ringing connections are effected in a manner which minimizes any undesired ringing at the subscriber locations and/or any failures to connect resulting from changes in the loop networks serving these locations.
It is yet a further object of the present invention to provide a telemetry system in which telemetry system information is automatically and easily developed based on user customer information and telephone system information and is readily accessible by the telemetry system user.